Bisbenzocyclobutene (BCB) was developed for use as a dielectric in semiconductor devices, specifically multi-chip module (MCM) applications. BCB is especially well suited for these applications because it adheres well to semiconductor materials such as silicon, silicon oxide, silicon nitride, aluminum, copper and polyimide. It is also used because it has a service temperature in excess of 300 degrees Celsius. These properties make BCB additionally desirable as a masking material, a protection layer and a wafer bonding material.
Despite the advantages of BCB, industry has avoided using BCB in many situations due to a significant practical problem related to BCB processing. The primary problem with the material is that it is resistant to wet chemical etching, particularly when the BCB has been fully cured. Because the BCB resists wet chemical etching, processing of BCB must be done by dry etching or plasma treatments. As is known by those skilled in the art, both of these processes commonly result in significant damage to the device leading to increased waste and excessive cost to the manufacturer. Consequently, many manufacturers have refused to incorporate BCB into semiconductor devices or have increased the cost of devices requiring the use of BCB to account for their own increased costs.
U.S. Pat. No. 5,879,572 entitled “METHOD OF PROTECTING SILICON WAFERS DURING WET CHEMICAL ETCHING,” discloses a process for micromachining silicon wafers using BCB as an etch mask. In this process, a film of partially cured BCB is applied over the metallization and circuitry on the wafer. The BCB protects these objects during wet chemical etching of the substrate. After etching of the substrate, the BCB is completely removed by dry etching or, because the BCB is only partially cured, a limited number of wet etch techniques. The present invention does not involve the application of a partially cured BCB protective layer. U.S. Pat. No. 5,879,572 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,204,081 entitled “METHOD OF MANUFACTURING A SUBSTRATE OF A LIQUID CRSTAL DISPLAY DEVICE,” discloses a process for etching a substrate using a light developable BCB protection layer. A mask is placed over the BCB layer, exposing only certain portions of the layer to a light source. The light source removes the exposed portions of the light developable BCB layer. The present invention does not use a light source to remove a BCB layer. U.S. Pat. No. 6,204,081 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,284,149 entitled “HIGH-DENSITY PLASMA ETCHING OF CARBON-BASED LOW-K MATERIALS IN AN INTEGRATED CIRCUIT,” discloses a plasma etching process for a BCB dielectric layer. A hard mask is placed over an upper BCB layer, the BCB layer being etched by a gas of oxygen, a fluorocarbon and nitrogen. The present invention does not use a gas to etch BCB. U.S. Pat. No. 6,284,149 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,514,872 entitled “METHOD OF MANUFACTURING A SEMICONDUCTOR DEVICE,” discloses a semiconductor having a BCB film applied over an insulating layer. The BCB film is fully cured and dry etched in an inductive coupled plasma reactive furnace. The present invention does not involve dry etching of a fully cured BCB layer. U.S. Pat. No. 6,514,872 is hereby incorporated by reference into the specification of the present invention.
As can be seen from the prior art, the difficulty with the use of BCB is that once it is fully cured wet etching techniques are ineffective. Because applications requiring precision processing often necessitate wet etching of the dielectric layer, and do not allow the substitution of partially cured BCB that may allow some degree of wet etching, BCB has been abandoned for many devices where it would otherwise be the ideal material. An example of such an application is the use of BCB as a wafer bonding material. It is therefore desirable in the art to have a method for effectively processing fully cured BCB with a wet etch process.